This invention relates to record players, and more particularly to a tone arm system by which to improve the quality of sound reproduction from sound-recorded discs rotated on a turntable and by which to improve the efficiency of mechanical movement of the stylus to and from such discs.
Historically, a tone arm, utilized to carry a cartridge stylus for reproducing the sounds recorded on a grooved disc rotating on a turntable, is supported on a hinged mount which allows the stylus to follow the vertical and horizontal motions required in reproducing the sounds contained in the grooved disc. In all cases, the operation of the hinge involves a degree of resistance determined by the coefficient of friction between the solid materials forming the bearings of the hinge. Thus, a coefficient of friction always is present, whether the hinge involves such structures as a direct sliding action of a shaft rotating in a cylinder, a pointed shaft rotated in a cone, a ball or roller bearing mount, the combination of a pointed shaft rotating on balls in a container, a conventional gimbal, a half gimbal with a rotating shaft in a cup, or a unit bearing utilizing a single ball mounted on a pedestal and supporting a tone arm carrying a cup which fits the ball.
The foregoing and other mechanical supports utilized heretofore for tone arms, are limited by the coefficient of friction between the materials. Such mechanical supports also transmit to the cartridge stylus transducer, not only mechanical noises caused by the inadequacies of the mechanical bearing supports to rotate freely, but also those sounds caused such as jars, bumps, vibrations and others originating at the supporting base for the turntable upon which the hinges are mounted. Even when such a base is isolated by rubber or spring mountings from an external cabinet, the sounds or vibrations felt by the base are transmitted along the tone arm to become reproduced along with the sounds recorded in the groove of the disc.
This undesirable sound transmission is due to the ability of the mechanical hinges to follow the motion of the supporting base. Directly mounted hinges follow the mounting base sounds exactly. Those hinges mounted in elastomeric sockets produce sounds which are limited in the frequency band to the lower end of the audible scale, but nevertheless these low frequency sounds are reproduced with the recorded sounds.
In addition to sounds transmitted through the mounting hinges, there is added the ability of the tone arm to vibrate resonantly, at a frequency transmitted to it through the mounting hinges and from the stylus sound. This resonance amplifies the effect of that sound as the stylus attempts to reproduce the sound in the groove of the recorded disc. Such resonance can appear as longitudinal motion along the tone arm as well as transversely across it.
Attempts have been made heretofore to reduce or modify this resonant tendency of the tone arm by use of materials such as wood, or by altering the shape of the tone arm. Although the use of wood reduces the Q, or increases the losses of the resonant arm, the resonance is not eliminated. Changing the shape of the tone arm, as by bending or curving, only increases the harmonic content of the tone resonated.
Additionally, tone arm systems of the automatic type provided heretofore utilize mechanical linkages and tracking mechanisms designed to interconnect the tone arm and associated turntable for inserting the stylus in the starting groove of a recorded disc and to effect removal of the stylus from the ending groove of the disc and return of the tone arm to a rest position. Such mechanical interconnections are subject to wear, and therefore require periodic maintenance and repair, and they contribute adversely to the generation of unwanted sounds.
Some manufacturers of tone arm systems have reverted to systems of the manual operating type in an effort to avoid the problems of drag and mass involved in the mechanisms for automatic operation. However, it is recognized that the human hand, even supported, is a clumsy, massive object with which to manipulate the characteristically delicate and light weight tone arm. Many scratched records and damaged stylii and cartridges, and the resulting distortions and other unwanted sounds, attest to this problem.